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KeepRite · Heat pump troubleshooting

Outdoor unit will not run or will not defrost - KeepRite heat pump defrost board (FAST 1173636/1177927/1190281)

What is going on

Checks on the time/temperature defrost board used in these heat pumps.

Likely causes

  • No 24 V on Y from the thermostat
  • Open pressure switch
  • Bad contactor
  • No 24 V on T1
  • Defrost thermostat stuck
  • Bad pigtail harness

Check in this order

  1. Unit will not run check 24 V at the Y input, then at the Y spade (goes out through the pressure switches to the contactor).
  2. Y spade has 24 V but the contactor is open: check coil voltage; none means an open pressure switch, voltage present means a bad contactor.
  3. Contactor closed but nothing runs check wiring, capacitor and compressor.
  4. No defrost jumper DFT to R, short the speed-up pins (timer runs 256x faster; 90 min setting takes about 21 s).
  5. Still no defrost confirm 24 V on T1 (fed once Y is on and switches are closed).
  6. During forced defrost, expect 24 V between C and W2; afterwards remove the DFT jumper or the unit will defrost every interval for the full 10 minutes.
  7. A stuck-closed defrost thermostat gives a 10-minute defrost every interval; stuck open means no defrost.

Applies to: KeepRite split heat pumps using FAST 1173636, 1177927 or 1190281 defrost boards

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Source: KeepRite_ICP_KeepRite_Tempstar_Heil_split_A_C_HP_R_410A_R_22_service_421_08_5400_04.txt - section Defrost Control Boards / Troubleshooting (FAST 1173636/1177927/1190281). Written in our own words; check the manual for your exact model.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.